GREENSBORO, N.C. — John Edwards’s trial on federal campaign finance charges kicked off here Monday with prosecutors painting the former presidential candidate as a practiced liar — and defense lawyers firing back that the case is based on shaky evidence from witnesses who have credibility problems of their own.

“It is said ambition is an important quality in a politician, especially one running for president. But like most things, it can be so consuming, a person can do anything he wants and won’t let anything stand in their [way] — not their family, not other people, not the law,” prosecutor David Harbach II said at the outset of his argument to the jury of nine men and seven women, including the four alternates.

Harbach argued that Edwards oversaw a scheme to have two supporters of his 2008 presidential campaign pay $1 million for luxury housing and other expenses for the mistress, Rielle Hunter, in order to keep his political prospects alive.

“He had to keep it quiet. If the affair went public, it would destroy any chance he had to be president, and he knew it,” Harbach said. “He made a choice to break the law — a very simple law that says the most a presidential candidate can accept [from any individual] is $2,300.”

“Edwards did what the evidence will show he always did … deny, deceive and manipulate,” Harbach contended.

To present his opening argument to the jury, Edwards turned to Allison Van Laningham, the most junior of the three attorneys defending him in the trial and the only woman at either counsels’ table. She argued that the gifts to Hunter were largely personal in nature and did not meet the legal standard to be considered campaign contributions.

“John Edwards is a man who has committed many sins but no crimes,” Van Laningham said in her opening. “We aren’t going to judge John Edwards for his sins.”

Van Laningham conceded that Edwards cheated on his wife, lied about having the affair and lied about not being the father of a daughter born to Hunter in 2008. But she said he did all those things for reasons an ordinary person might — and that trying to win the presidency had nothing to do with it.

“John Edwards did not hide his mistress for any purpose related to the election; he did it for the same reason anyone would. He did it to hide it from his wife,” to protect his family and to avoid personal humiliation, she said.

The defense lawyer said Young and his wife diverted hundreds of thousands of dollars from wealthy supporter Rachel “Bunny” Mellon to pay for a new home. She said that Young lied repeatedly about the matters at issue, including when he falsely claimed to be the father of Hunter’s daughter and that Young is hoping to profit from a movie deal about the case.

Van Laningham said Young and Button plotted to take revenge on Edwards and schemed to plant media stories they hoped would produce a drumbeat for the indictment of the former senator and 2004 Democratic vice presidential nominee.

Young took the stand Monday afternoon as the prosecution’s first witness and testified about his personal background, as well as his first encounters with Edwards, Hunter and Mellon.

Already, there’s been new controversy surrounding Young. In her opening, Van Laningham mentioned that the former Edwards aide reached out to three people, and in motions filed under seal over the weekend and brought up by the judge outside presence of jury, those defense witnesses include one person he allegedly had a one-night stand with in 2007.

During a court session preceding the argument, the judge ordered defense not to mention that alleged fact in opening arguments but didn’t completely rule out allowing Young to be cross-examined about it, and he’s expected to be asked whom he’s been in contact with when he takes the stand.

Edwards faces six federal felony charges in connection with the payments of Hunter’s expenses and the failure to report them to the Federal Election Commission.

Edwards, clad in a dark-blue suit and blue tie, looked dour but attentive during the arguments. During the final process of jury selection earlier Monday, Edwards — who made a fortune as a trial attorney himself — was an active participant, glancing at the jurors over his reading glasses, frequently whispering to his attorneys and occasionally turning to the gallery to talk with his adult daughter, Cate.

In his opening, Harbach acknowledged that Edwards’s decision to have an affair with Hunter is not what jurors are being asked to pass judgment upon.

“It is not a federal crime to have an affair,” the prosecutor said. He said Edwards knew about the payments from his national finance chairman, Fred Baron, and Mellon.

Baron died days before the 2008 election. Mellon, now 101, is frail and is not expected to testify.

Van Laningham said Edwards was unaware of the payments from Mellon at the time she made them but eventually figured out that Baron was supporting Hunter. She repeatedly argued that the money — much of which went to pay for luxury hotels — was intended for more mundane expenses, such as “food and medical care” for Hunter, her pregnancy and her son.

Until Monday, defense lawyers had given no indication publicly about whether Edwards will take the stand in his own defense, but Van Laningham seemed to indicate in her opening that he will.

“John Edwards has maintained his silence,” she said. “That silence ends today. … The truth for John may be a sin, but it is not a federal crime.”